German Published Patent Application No. 103 10 492 describes that an electric motor responsible for steering assistance is connected by a belt transmission to a ball-screw transmission for displacing vehicle wheels. An output shaft of the electric motor and a ball nut of the ball-screw transmission are each connected to a belt pulley (or toothed disk). The belt pulley of the output shaft of the electric motor is connected to the belt pulley of the ball nut via a belt, so as to be able to drive it. The ball thread converts the rotation of the ball nut into a translational movement of the screw of the ball-screw transmission, or of the gear rack.
The ball nut is supported by a cam in a steering-gear housing such that the center-to-center distance between the output shaft of the electric motor and the screw or the gear rack is variable. The tension of the belt of the belt transmission can be adjusted by rotating the cam (which is, therefore, a part of the ball nut and belt pulley).
Alternatively, or in addition to that, German Published Patent Application No. 103 10 492 also allows the electric motor to be supported via a cam such that the center-to-center distance between the output shaft and the screw or the gear rack is variable.
The belt adjustment is of particular importance to the functioning and the operational reliability of the steering system. When the belt tension decreases, the belt may jump, slip, or become disengaged in some other manner. Consequently, the power-steering system is no longer completely operational.
Influences leading to a decrease in the belt tension can vary as a function of the implementation of the design. For example, a decrease in the belt tension may result from torques that are made up of the belt tension itself, with the eccentricity as a lever arm. However, friction torques from the bearing or torques from the belt transmission, which can lead to a decrease in the belt tension, are also possible. A reduction in the belt tension may also be produced by vibrations during assembly or operation.
Therefore, in order to avoid affecting the operativeness of the power-steering system, a change in the belt tension must be reliably prevented during the further assembly and the operational life of the steering system.